Lubricating grease composition



Patented Nov. 13, 1951 2.575.286. wnmoa'rma GREASE 'comrosrr'ron Arnold J. Money, Clark-Railway, and Paul V. Smith, Jr., Westfleld, N. 1., asaignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application July 29, as,

i cam Serial 1 This invention relates to a lubricating grease composition and more particularly to high temperature anti-friction bearing lubricating greases which are suitable for high temperature use. More particularly, the invention relates to a high temperature grease prepared from a lubricating oil thickened with an alkali metal soap of a higher fatty acid. in conjunction with an alkali metal salt of a low molecular weight oxy acid.

It has been suggested in the prior art that for some purposes, it is advantageous to combine certain metal salts, particularly the metal salts of organic acids of low molecular weight, with the metal soaps which are ordinarily employed as thickeners for lubricating grease compositions. Various investigators have round that the addition of metal salts oi the character referred to have utility for improving stability and high temperature properties, and the like. There appear to be several theories as to the operation of such metal salts in conjunction with the metal soaps. One such theory is that the addition of salts of low molecular weight acids to soaps oi! relatively high molecular weight results in the formation of a complex with superior grease thickening eilect and improved stability.

Whatever may be the phenomena involved, the addition of salts of low molecular weight compounds appears to be particularly advantageous in connection with greases of alkali and alkaline earth metal soap bases. The low molecular weight salts appear in many cases, at least, to improve the physical structure of the grease. Compositions of this character are particularly receptive to the action of oxidation inhibitors and it is possible that the compositions themselves are more stable against oxidation than greases thicknened with soaps of high molecular weight carboxylic acids alone for example.

Suggestions in the prior art have included the use 01' metal salts of low molecular weight carboxylic acids which are saturated, such as acetic and propionic acids, and even more recently it has been suggested that certain of the lower unsaturated acids, such as acrylic acid, and crotonic acid and the like may be used as soap thickener adjuncts.

According to the present invention, the salts of certain low molecular weight oxy acids are highly useful as ingredients of lubricating reases.

It is the object 01! this invention, therefore, to prepare an improved grease suitable for antiiriction bearing and related surfaces at elevated temperatures, 1. e., temperatures in the neighborh of from 30010 350 and even higher. A

"Claims. ((1253-41) iurther object of the invention is to provide a lubricating grease composition comprising a lubricating oil thickened to a grease consistency with a combination oi the alkali metal soaps 0! low molecular weight oxy acids and high molecular weight aliphatic acids.

The low molecular weight oxy acids which are employed in this invention contain an ether linkage and in this respect are similar to furoic acid, which is a heterocyclic unsaturated acid containing an ether linkage in a 5-membered ring. In fact, greases prepared by employing salts 0! alkoxy acids such as ethoxy propionic acid are in many respects similar to the excellent high dropping point greases prepared from Iuroic acid. Other acids containing oxygen-are apparently quite different. For example, when levulinic acid is employed, this acid having an oxygen atom in a ketonic linkage, greases are formed of relatively low dropping point, similar to the greases containing saturated straightchain acids having no oxygenin the hydrocarbon chain. In addition, the soaps oi levulinic acid and straight chain aliphatic acids are difllcult to disperse in mineral oil even at elevated temperatures. The structure of the oxy acids mentioned above are shown below:

Mol. weight 1 11s cm-cm-o-om-cm-coon Ethoxy propionic acid 112 O-CH=CHCH=CC 0 OH Furoic acid OIL-Pi-CHr-CHr-C 0 0H Levulinic acid 116 CHr-CHr-CHrCHrCHr-COOH 'Caproic acid -Ethoxy propionic acid, which is the preferred of the low molecular weight oxy acids operable in this invention, may be prepared from betapropiolactone by reaction with ethyl alcohol. The beta-propiolactone may be prepared from formaldehyde and ketene. The preparationof this acid is described in the Journal of American Chemical Society. vol. 70, pa es 998-1006 (1948) It may also be prepared by adding ethanol to acrylonitrile or acrylic esters followed by hydrolysis or by the reaction of an alkali ethoxide with B-halopropionic acid.

The oxy acids which are employed in the greases oithis invention have the formula:

- acreage a' and R" being saturated aliphatic radicals and R and R" containing a total of at least 2, and

not more than 7 carbon atoms. B. may be methyl,

ethyl, propyl, isopropyl, n-butyl, isobutyl, sec. butyl, t-butyhamyl, etc. while R" may be'similar divalent groups. Specific mention may be madeof methoxy propionic acid, ethoxy propionic acid, nand iso-propoxy propionic acids, nand isopropoxy acetic acids-and secondary butoxy acetic with the desired lubricating oil an alkali metal salt of a low molecular weight oxy acid with an alkali metal salt of a high molecular weight substantially saturated aliphatic acid. In general, the metallic element of the salts as well as of the soaps may be any of the alkali metals. sodium. however, is the preferred embodiment of the invention. It is within the concept of the invention, however, to use mixtures of sodium and lithium, i. e. the sodium salt of the low molecular weight oxy acid may be used in conjunction with the lithium salt of the high molecular weight saturated fatty acid and vice versa.

The relative proportions of the high molecular weight soap and of the low molecular weight salt may be varied rather widely. In molecular proportions, it is preferred to use 1 to 3 parts of the soap with about 1 to 2 parts of the salt. In general, however, it is preferable that the molecular proportions be more nearly equal and specifically, proportions of about 1 to 1 appear to be the most satisfactory. Further, the quantity of the soap and salt ingredients to be used in a given grease composition vary with the type of grease which is desired and also with the kind and the viscosity of the oil which is used as a liquid base. For a still grease composition, the total quantity of soap and salt may approach 50% of the weight of the final composition. on the other hand, for a soft grease, the total proportion of soap and salt may be as low as about 5% based on the weight of the entire composition.

In general, the grease should consist of a lubricating oil having a viscosity of about 35 to 200 S. S. U. at 210 F. containing about 3 to 30% by weight of the metal soap of a Cl: to C2: of fatty acid or glyceride along with 2 to 20% by weight of the metal salt of the low molecular weight oxy acid. In general, ethoxy propionic acid is preferred to form the low molecular weight oxy acid portion. However. as it was pointed out above, other oxy acids, such as methoxy propionic acid and propoxy propionic acid may be used.

For ordinary anti-friction bearing greases, the sodium soap and the sodium salt of ethoxy propionic acid are specifically preferred.

In the preferred embodiment of this invention a substantially saturated fatty acid having an average chain length in the range of 12 to 22 carbon atoms is utilized, however any of the fatty acids known in the art of grease manufacture may be employed. For ease of dispersion generally the higher molecular weight acids are preferred. These preferred acids consist predominantly of acids having a carbon chain length of 18 or slightly higher. They may be natural products such as stearic. arachidic. or the hydrogenated acids obtained from tallow or fish oil acid fractions.

For the liquid phase of the grease, mineral base lubricating oils are preferred but the invention is not necessarily limited to the mineral base oils. Various synthetic oils may also be used. As is fweu known in theart of grease making, certain synthetic esters, especially the dlbaslc acid esters. such as dl-Z-ethyl-hexyl sebacate and homologous and analogous esters are preferred for certain purposes ingrease making. --According to this invention-the lithium soap grease of such compounds, modified with the sodium or lithium salts of ethoxy propionic acid, and the like, are particularly useful for lubrication at very low temperatures. Other synthetic oil base greases such as those-employing the polyglycok or the glycol ethers are also contemplated as being within the scope of this invention. The combined soaps and salts may be used to thicken mixtures ofmineral oil and synthetic oil as well as being useful with either type of oil alone.

As an example of the concept of this invention, a grease composition containing the ethoxy propionic acid and its properties are described below:

Formulation:

Method of preparation The hydrogenated fish oil acids and V3 01 the mineral oil were charged to a fire heated grease kettle and the temperature raised to 150 F. The ethoxy-propionic acid was charged and the acids immediately coneutralized with a 30% aqueous solution of sodium hydroxide. The temperature was raised to 220 F. and when the soap concentrate was fairly dry additional oil was slowly added while raising the temperature to 440 F. All of the oil should be added by this time. The phenyl alpha naphthylamine was added and the grease drawn into pans for cooling. The cold grease was returned to the kettle for homogenization and then filtered and packaged.

Properties Per cent free alkali, 0.12 as NaOH.

Appearance, yellow-smooth short fiber.

Dropping point, F., 446.

Worked penetration, mm./10, 306.

Structure stability to mechanical working, penetration after 100,000 strokes, fine hole worker plate, 339 mm./ 10.

Water washing test 1?. water temperature) per cent loss, 0.0.

Wheel bearing test, 6 hours at 220 F., pass; conditions and lubrication excellent.

High temperature spindle test, 204 bearing, 10,000 R. P. M., 300 F., 400 hours; bearing failure grease in good condition.

For comparison tests on greases having similar formulations but employing, furoic, ethoxy propionic,'levulinic and caproic acids respectively are given below:

Basic formulation 6.0% low molecular weight acid.

15.0% hydrogenated fish oil acid.

4.4% NaOH.

73.6% mineral oil with a viscosity at 210 F. of

500 S. S. U.

1.0 phenyl alpha naphthylamlne.

amazes Emmi r i Le ul'ni Propionic mo v 1 c Caproic Acid Acid Acid Acid Per Cent Free Alkalinity 0.12 0.06 0. 27 0.25 Worked Penetration (77 F.) 306 234 358 Grease did not make. Structural Stability (Penetration 100,000 339 I 272 Semi Fluid" Soap separates out.

Strokes in worker). Dropping Point, "F 446 488 378 Dispersability oi Soap Excellent. Fair Poor Wheel Bearing Test, 6 hours at 220 F Pass Pass.... Fail The above results show that the sodium soap of ethoxy propionic acid in combination with the sodium soap of hydrogenated fish oil acids is easy to disperse and gives an excellent grease of high dropping point and structural stability which is somewhat softer than the furoic acid product.

To summarize briefly, this invention comprises the formation of an improved high temperature 2 lubricating grease composition which consists essentially of a lubricating oil base thickened to a grease consistency with the desired amount of the alkali metal salt of a low molecular weight oxy acid, in conjunction with the alkali metal 2 salt 01' a high molecular weight saturated aliphatic acid.

What is claimed is:

1. A lubricating grease composition consisting essentially of a lubricating oil thickened to a grease consistency with from 5 to by weight of a mixture of an alkali metal soap of a high molecular weight fatty acid and an alkali metal salt of a low molecular weight oxy acid having the general formula:

wherein R and R" are saturated aliphatic radicals and R plus R" contain a total of at least 2 and not more than 7 carbon atoms.

2. A lubricating grease composition according to claim 1 wherein said low molecular weight oxy acid is ethoxy propionic acid.

3. A lubricating grease composition according to claim 1 wherein said low molecular weight oxy acid is methoxy propionic acid. a

4. A lubricating grease composition according to claim 1 wherein said low molecular weight oxy acid is propoxy propionic acid.

5. A lubricating grease composition consisting essentially of a mineral base lubricating oil thickened to a grease consistency with from 3 to 20% by weight, based on the total composition or an alkali metal soa of a mixture of aliphatic substantially saturated fatty acids having an average carbon chain length within a range of from 12 to 22 carbon atoms and from 2 to 15% by weight of an alkali metal salt of ethoxy propionic acid.

6. A composition according to claim 5 wherein said alkali metal soap is sodium soap and said alkali metal salt is sodium salt.

7. A composition as in claim 1 wherein said lubricating oil is a synthetic ester oil.

8. A lubricating grease composition suitable for high temperature service consisting essentially of a lubricating oil thickened to a grease consistency with substantially equal molar proportions of an alkali metal salt of ethoxy propionic acid and an alkali metal soap 0! a mixture of substantially saturated fatty acids having an average carbon chain length within a range of from C1: to C22.

9. A composition according to claim 8 wherein said alkali metal salt is sodium salt and wherein said alkali metal soap is sodium soap.

10. A lubricating grease composition consisting essentially of 6% by weight ethoxy propionic acid, 15% by weight of a mixture of hydrogenated, substantially saturated, flsh oil acids, having an average chain length within a range of from C1: to C22, 4.4% by weight sodium hydroxide, 73.6% by weight of a coastal type mineral lubricating oil having a viscosity at 210 F. of S. S. U. and a minor amount of phenyl alpha naphthylamine.

ARNOLD J. MORWAY. PAUL V. SMITH, JR.

REFERENCES crrEn The following references are of record in th file of this patent:

UNITED STATES PATENTS Number 'Name Date 2,468,098 Morway et al. Apr.-26, 1949 2,487,080 Swenson Nov. 8, 1949 OTHER REFERENCES Serial No. 361,581, Giloy (A. P. 0.), published May 25, 1943. 

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH FROM 5 TO 20% BY WEIGHT OF MIXTURE OF AN ALKALI METAL SOAP OF A HIGH MOLECULAR WEIGHT FATTY ACID AND AN ALKALI METAL SALT OF A LOW MOLECULAR WEIGHT OXY ACID HAVING THE GENERAL FORMULA: 